Analysing the Causes of Increased Large Unstained Cells (LUCs) Percentage in WBC Differential

Background and Aims: Large unstained cells (LUCs) are peroxidase negative mononuclear cells which include large lymphocytes in healthy individuals, peroxidase negative blasts, plasma cells and atypical lymphoid cells. This study aims to assess the causes for elevated LUC% in ADVIA 2120i by rapid peripheral smear review. Materials and Methods: All consecutive anticoagulated blood samples with LUC% >4%, from June 2022 to March 2024, were processed in ADVIA 2120i, and demographic factors, LUC parameters and peripheral smear observations were documented under six diagnostic disease categories. Statistical analysis was performed using SPSS software (IBM, 28.0). Results: The median LUC count of 0.5 × 10 3 cells/µL with an inter-quartile range of 0.2–2.3 × 10 3 cells/µL of blood was observed in haematolymphoid neoplasms. There was a significant overlap of %LUC values among different categories. The majority (69.6%) had % LUC between 4.1% and 9.9%. Marked elevations were observed in AML, CML, ALL and infections. Conclusion: Absolute LUC count could be used as a cost-effective and readily available marker to identify a case of clinically suspicious haematolymphoid neoplasm with LUC count more than or equal to 0.5 × 10 3 cells/µL of blood in conjunction with other complete blood count parameters. However, reflex peripheral smear testing is mandatory in the current setting for confirmation.